Project Summary Idiopathic pulmonary fibrosis (IPF) remains a devastating fibrotic parenchymal lung disease with high morbidity and mortality, for which there are no effective therapies. Consequently, it becomes increasingly important to identify molecular pathways that are targetable for therapeutic intervention. This proposal seeks to address this unmet need by investigating the role of TNF- in the resolution of pulmonary fibrosis using the well- characterized bleomycin model in mice. In preliminary studies we have shown that the intratracheal administration of TNF- at the peak of the bleomycin-induced fibrotic response accelerates resolution and that mice with a genetic TNF- deficiency have impaired resolution of fibrosis. These and other considerations have led us to hypothesize that TNF- plays an integral role in the resolution of pulmonary fibrosis through effects on macrophages and myofibroblasts. We hypothesize that TNF- alters the phenotype of both of these cell populations reducing their pro-fibrogenic phenotype and allowing them to aid in the resolution process. Specific aim 1 will address the hypothesis that TNF- induces a switch in macrophage programming from alternative to classical, reducing the production of pro-fibrotic mediators including TGF- and IGF-I, increasing pro-inflammatory cytokine production (TNF-) and enhancing matrix metalloproteinase production to initiate tissue remodeling and the restoration of normal pulmonary architecture. The goal of specific aim 2 is to address the hypothesis that TNF- promotes myofibroblast apoptosis in a two-step process, first by directing myofibroblasts de-differentiation to fibroblasts, and second by sensitizing these fibroblasts to undergo Fas- mediated apoptosis. Finally, specific aim 3 will translate our work into human disease using IPF-derived myofibroblasts and a humanized mouse model of fibrosis. Our proposed studies represent the first time TNF- has been investigated as a key player in the resolution process of pulmonary fibrosis. It also represents a novel opportunity to identify new therapeutic targets for the treatment of IPF. Thus, a long-term goal of this proposal is to translate our anticipated findings into the development of therapies for patients diagnosed with fibrotic lung diseases, including IPF.